A380 vs ADC12 Aluminum: Which Die Casting Alloy to Specify

Most aluminum die casting drawings that reach us specify one of two alloys, and about a third of them specify the wrong one. Usually the drawing was copied from a previous program, or the material line says A380 because the designer works in Ohio and ADC12 because the designer works in Osaka. Both alloys are excellent. They are not interchangeable, and the difference shows up first in thin walls and second on the machining line.

Here is what actually separates them.

The short answer

Specify A380 if the part carries a lot of machining, if walls are 2 mm or thicker, or if the supply chain is North American. Specify ADC12 if any wall is under 2 mm, if the flow path is long relative to wall thickness, or if the supply chain is Asian. If the part lives outdoors or has to hold pressure, specify neither and go to A360.

Standards lineage: same family, different rulebooks

Both alloys belong to the aluminum-silicon-copper branch of the aluminum-silicon alloy family. They diverge in which standards body wrote them down.

Two cautions on that table. ADC12 is often quoted as “equal to A383”, and for composition and behaviour that holds well enough to swap between them on most parts, but they are separate specifications with different tin and nickel ceilings. And EN AC-47100 is the nearest European grade, not a drop-in match, because it caps copper at 0.7 to 1.2% against ADC12’s 1.5 to 3.5%. A part qualified in ADC12 and then sourced against EN AC-47100 will lose measurable strength.

Composition side by side

Mass percent, aluminum as remainder.

Three lines in that table matter more than the rest.

Silicon is the difference that controls castability. ADC12 runs 2 percentage points higher at minimum and can reach 12.0%.

Copper is the difference that controls strength, machinability and corrosion. Note that the ranges overlap: an ADC12 heat certified at 3.4% copper is chemically close to A380 and will behave like it. If copper content matters to your application, cap it on the drawing rather than trusting the grade name.

Zinc is the quiet one. A380 tolerates up to 3.0% zinc while ADC12 caps it at 1.0%. High zinc is a signature of heavily recycled secondary metal, so the tighter ADC12 ceiling gives a small amount of built-in protection against poor ingot quality.

Mechanical properties

Typical as-cast values for high pressure die castings.

These are the numbers to design against, with one important qualification: they are measured on separately cast test bars, not cut from your part. A 4 mm section with shrinkage porosity at its thermal centre will not deliver 324 MPa regardless of what the certificate says. The 4 to 6% property gap between these alloys is smaller than the variation caused by wall thickness and gating, which is why alloy choice should follow castability rather than the datasheet.

Two practical notes. The density difference is small per part but not per program: a 400 g housing is 6 g lighter in ADC12, which is 1.2 tonnes of aluminum across 200,000 parts a year. And both alloys sit at 96 W/m·K, so neither is the right choice for a thermally driven part. Cast heatsinks belong in A360 at 113 W/m·K or A413 at 121 W/m·K.

Why higher silicon gives ADC12 better fluidity

Both alloys are rated “excellent” for castability, which flattens a real difference. ADC12 fills thin sections better, and the mechanism is worth understanding because it tells you when to care.

The aluminum-silicon eutectic sits at 12.6% silicon and 577 °C. An alloy at that composition freezes at a single temperature. Move away from it and the alloy freezes across a temperature interval instead, growing primary aluminum dendrites into the liquid as it cools. Those dendrites are what stop flow: once the advancing metal front is roughly 20 to 30% solid, it stops behaving like a liquid and stalls.

ADC12 at 9.6 to 12.0% silicon sits close to the eutectic, so its freezing range is narrow and it stays genuinely liquid until late. A380 at 7.5 to 9.5% silicon has a wider freezing range and starts building dendrites earlier in the flow path.

Silicon adds a second effect. Its latent heat of fusion is roughly 1,810 kJ/kg against 397 kJ/kg for aluminum, so a higher-silicon melt carries substantially more stored heat to release during solidification. More latent heat means more time before the front freezes.

In practice this shows up as:

• Minimum wall. A380 is comfortable at 1.5 mm. ADC12 gets to 1.0 to 1.2 mm on small parts, which is the low end of our achievable range.
• Flow length. A spiral fluidity test typically shows ADC12 running 10 to 15% further than A380 at the same superheat.
• Cold shut margin. On a long thin part, ADC12 gives a wider process window before you start seeing cold shuts and misruns, two of the defects catalogued in common aluminum die casting defects.
• Shrinkage. Silicon expands slightly on freezing, partly offsetting aluminum’s roughly 6% volumetric contraction. Higher silicon therefore means less solidification shrinkage, which helps both dimensional repeatability and shrinkage porosity in moderately thick sections.

If every wall on your part is 2.5 mm or thicker with a short flow path, none of this matters and the choice should be made on machining and cost. If you have a 1.5 mm wall 180 mm from the gate, it decides the program.

Why A380’s copper buys strength and machinability, and costs corrosion

Copper is A380’s differentiator, and it cuts both ways.

Strength. Copper forms Al2Cu, which strengthens the matrix even in the as-cast condition. That is the whole of A380’s 14 MPa tensile and 9 MPa yield advantage. It also lifts hardness from 75 to 80 HB.

Machinability. A380 is rated very good, ADC12 good, and there are two reasons. First, a slightly harder matrix produces a cleaner chip and less smearing at the cutting edge. Second, and more important, ADC12’s near-eutectic silicon means more and coarser primary silicon particles, and silicon particles are abrasive. Cutting ADC12 with the same insert and parameters as A380 typically gives 20 to 30% shorter tool life. On a heavily machined casting that shows up directly in price, which is why our machining after casting quotes differ between the two alloys on the same geometry. High-silicon alloys machine well with PCD or diamond-coated carbide, but those tools cost more.

Corrosion. This is where copper hurts. Al2Cu particles are cathodic to the surrounding aluminum, creating galvanic microcells that drive pitting in humid or chloride environments. Both alloys rate “fair” and neither belongs in bare outdoor service. A380 at 3.0 to 4.0% copper is the worse of the two, though the practical gap narrows once you account for the overlapping ranges.

If corrosion resistance is a genuine requirement, do not try to pick between these two. Move to A360, which caps copper at 0.6% and rates good for corrosion and excellent for pressure tightness. Alternatively, accept the alloy and solve it with coating: chromate conversion, powder coat or wet paint through surface finishing all perform well on both grades. Note that neither alloy anodizes to a decorative appearance; high-silicon castings anodize grey and mottled.

Regional availability and cost

The cost delta between these alloys almost never changes a program’s economics. Availability sometimes does. A 3,000-piece-per-year part cast in Dongguan against an A380 requirement may add a procurement step that a 300,000-piece-per-year part would absorb without noticing. Say on the drawing whether an equivalent grade is acceptable, and you keep that option open.

One rule that applies to both: never let a foundry mix runner returns between alloys. Copper and zinc from A380 returns will drift an ADC12 melt out of specification within a few charges, and the failure shows up as unexplained property variation months later.

Specify this one when

Specify A380 when

• The part carries substantial machining and tool life drives cost.
• Walls are 2 mm or thicker with a reasonable flow path.
• The yield strength budget is tight and you need every one of the 159 MPa.
• The supply chain, prints and quality documents are North American.
• Cost per kilogram is the primary lever and the geometry is casting-friendly.

Specify ADC12 when

• Any wall is below 2 mm, or the flow path is long relative to wall thickness.
• The part is a thin-wall electronics or instrument housing with a large flat face.
• The supply chain is Asian and you want the most widely stocked grade.
• Slightly lower weight per part matters at volume.
• Existing drawings, PPAP documents or a predecessor part already specify JIS grades.

Specify neither when

• Outdoor, marine or humid service requires real corrosion resistance. Use A360.
• The part must hold pressure or achieve an IP seal without impregnation. Use A360.
• Heat dissipation drives the design. Use A360 at 113 W/m·K or A413 at 121 W/m·K.
• The drawing requires T6 heat treatment or structural welding. No die casting alloy will do this; the part needs to be machined or forged.

What to write on the drawing

A material line that actually protects the program looks like this:

MATERIAL: ADC12 PER JIS H 5302 (ASTM A383 ACCEPTABLE AS EQUIVALENT)
  Fe 0.8-1.1% FOR DIE SOLDERING CONTROL
  Cu 2.5% MAX
  MATERIAL CERTIFICATE REQUIRED PER LOT

Three reasons for the extra lines. Iron below roughly 0.8% lets the casting solder itself to the steel die, and iron above 1.1% cuts ductility, so pinning the range is worth more than most designers realise. Capping copper inside the ADC12 range is how you get the corrosion behaviour you actually want instead of the behaviour the range allows. And a per-lot certificate is the only way to detect the slow chemistry drift that comes with heavily recycled secondary metal.

Whichever grade you land on, the wall thickness, draft and fillet rules that determine whether it casts cleanly are the same for both, and they are set out in the aluminum die casting design guide.

We cast both alloys daily on 160 to 1,250 ton machines and hold stock of both in Dongguan. Send your 2D and 3D files to our engineers through contact and the DFM report will include an alloy recommendation with the reasoning, along with anything in the geometry that would change the answer.